Administering a typhoid Vi conjugate vaccine to residents in poor countries would be cost-effective in settings in which the incidence of the infection is 50 cases/100,000 annually, based on a computer model that takes into account various vaccination strategies.

Investigators reached that conclusion by creating a dynamic, age-structured transmission model that mimicked several vaccination strategies.

The model simulated 10-year programs that involved routine immunization of infants younger than age 1 year using the Expanded Program on Immunization (EPI), and adding a 1-time catch-up program for children aged 5 to 14 years.

The immunization model that used EPI and more than 50 cases/100,000 was highly cost effective. Adding the catch-up component was cost effective when the annual incidence was >130 cases/100,000.